The narrow adit is permanently flooded, so after descending a long staircase, access to the cave is made by boat.

At the end of the adit, the cavern opens up with fluorspar veins, stalactites and stalagmites, and the so-called "Bottomless Pit".

This chamber has an underground lake with a 20 metres (66 ft) high waterfall and an extremely deep vertical shaft, now choked to within 20 metres (66 ft) of the surface by rock spoil dumped by miners, after driving the continuation of the canal to the natural streamway beyond, which provided the bulk of the water for the canal.

[3] At the foot of Winnats Pass, it is a tourist attraction with an underground boat trip to the cavern.

A connection was discovered in 2006 between the Speedwell Cavern system and Titan, the largest natural shaft in the UK, which is 141.5 metres (464 ft) high.